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Coastal Engineering: Theory and Practice
Calculation of pressures:
1. Active earth pressure
= Kax unit weight of soil x height
= 0.237 x 19.5 x 6.8
= 31.42 kN/m2.
2. Pressure due to surcharge load = 0.237 x 30 kN/m2.
= 7.11 kN/m2
3. Pressure due to water
= 10.03 x 4 = 40.12 kN/m2.
Calculation of forces:
(1) Active earth pressure = 0.5 x 6.8 x 31.42 = 106.83 kN/m. acting
@ 2.27 m from bottom as variation of pressure distribution is triangular
(2) Force due to surcharge load = 0.5 x 6.8 x 7.11 = 24.174 kN/m. @ 2.27 m
from bottom
(3) Force due to water = 40.03 x 0.5 x 4 = 80.06 kN/m. @ 1.33+0.5 m
from bottom
(4) Berthing force = 100 kN/m. © 6.8 m from bottom
(5) Mooring force = 15 kN/m. @ 6.8 m from bottom
Calculation of Résultant force:
Both mooring and berthing force would not impart at the same time.
Considering only the Mooring force,
Active résultant force, Ra — +106.83 + 24.174 — 80.06 + 15,
Ra = 65.94 kN/m.
Similarly, when berthing force alone is taken into account,
Total résultant force, Ra = 106.83 + 24.174 — 80.06 — 100
Ra = -49.05 kN/m.
Design is carried out for the critical case having high magnitude of force.
Hence we consider mooring force only case.
Calculation of centroid distance:
To find point at which résultant force acts,
_ 106.83 x 2.27 + 24.174 x 2.27 - 80.06 x 1.833 + 15 x 6.8
y = ---------------- --------------------------------------------- -------- —
65.94
ÿ = 3.83 m from bottom of the wall.